The use of machines to provide a controlled resistance to bodily muscle function for the purpose of exercising and training is well known. In part, such machines are adapted to simulate barbells and other such weights traditionally used for weight lifting exercise. The machines disclosed in Uyada, et al., U.S. Pat. No. 4,317,566; Uyada, et al., U.S. Pat. No. 4,339,125; and Mezman, U.S. Pat. No. 3,905,599, are typical. The machines shown in these patents employ levers moved by the person exercising in such a way that weights are lifted. The weights involved are arranged in a stack of flat, brick-like weights. Movement of the lever by the person exercising causes a vertically oriented bar to move upwardly. A selected number of weights may be engaged with the bar so as to be lifted by the user by thrusting a pin through a hole in the weight and on through a corresponding hole in the vertical bar. This arrangement for attaching weights is common. When the user of the machine wishes to change the amount of weight that is being lifted, the user typically must pause to change the location of the pin to engage more or fewer weights. The user of an exercise machine typically places himself at a particular location with respect to the machine, hereinafter referred to as the "exercise station," where he sits, stands, or lies so oriented as to operate the levers or comparable devices that must be moved to exercise. The exercise station is usually remote from the stack of weights.
In certain exercising routines, it is considered desirable to lift a series of weights in direct succession, each weight being slightly heavier than that preceding it. This procedure is called "pyramiding." Pyramiding cannot be smoothly and easily carried out on an exercise machine when the user must pause between each effort, leave the exercise station, and go to a different location relative to the machine to change the amount of weight being lifted. Consequently, with machines such as those shown in the cited patents, a second person typically must be stationed beside the weights to tend them. In addition to the disadvantage of requiring a second person, the procedure outlined also places that second person near moving parts of the machinery where cables, levers, and dropping weights can present hazards to health.
Pneumatic and hydraulic cylinders have been employed in exercising machines. Thus, hydraulic or pneumatic cylinders have been used to provide a force against which the exerciser must exert himself, the hydraulic or pneumatic cylinders being effectively substituted for the stack of weights used in the machines discussed above. Examples include Jenkinson, U.S. Pat. No. 4,353,547; Wilmarth, U.S. Pat. No. 4,397,462; Keiser, U.S. Pat. No. 4,257,593; Ariel, U.S. Pat. No. 4,354,676; and Wilson, U.S. Pat. No. 4,063,726. Instead of engaging or disengaging weights to be lifted, pressure in the hydraulic or pneumatic cylinder is changed to increase or decrease the resistance provided by the machine to a user's exertions.
Exercise machines tend to operate cyclically. A weight is lifted and then returned to its original position, a spring is compressed and rebounds, the air in a cylinder is compressed and allowed to expand, and so forth. Such a cycle shall be referred to herein as a "stroke" in the use of an exercise machine. In certain therapy and training regimens, it is considered beneficial to vary the resistance being offered by the machine to the user's efforts within various parts of the stroke. In other instances, resistance is adjusted to vary in proportion to the force being applied by the user, the speed of movement, the acceleration, and so forth. The machines disclosed in Ariel and Wilson vary hydraulic pressure or the like under electronic control to achieve the desired pattern of resistance. Jones, U.S. Pat. No. 3,998,454; and Jones, U.S. Pat. No. 3,858,873 disclose noncircular cams that turn and take up cables or chains that in turn are connected to weights. As a consequence of this structure, force is applied by the cable or chain to the cam with varying moment arms. Thus, cams can be designed to cause the resistance experienced by one attempting to turn the cams to vary in a predetermined pattern.
When a weight is lifted and then returned to the floor, the weight lifter must first contract muscles in the manner necessary to lift the weight and then must relax the muscles in a controlled way to lower the weight again without dropping it. A stroke on an exercising machine also typically involves a first part, during which muscles are being contracted until a maximum degree of contraction is reached, and a second part, in which the muscles are relaxed in a controlled manner, which exerts continued resistance to the force being overcome, as the user's limbs are returned to the beginning position and the stroke is completed. The first part will sometimes be referred to herein as the "contraction portion" of a stroke, and the second part as the "relaxation portion."
In many instances, an exerciser is capable of utilizing more weight or withstanding a greater force in the relaxation portion of a stroke then in the contraction portion. Furthermore, in certain exercising, therapeutic, and training regimens, it is considered especially beneficial to increase the weight or force against which the muscles of the exerciser must act in the relaxation portion as opposed to the contraction portion of the stroke. By this means, the muscles can be exercised to the maximum throughout the stroke. As a consequence, the same amount of therapeutic or training effect may be achieved in less time or fewer strokes than would be necessary if the weight or force to be resisted is held constant throughout the stroke. Weight or force held constant throughout a stroke may be referred to as "concentric" weight or force. Weight or force added primarily for the relaxation portion of a stroke may be referred to as "eccentric" weight or force.
It is known to add eccentric weight in weight training when barbells or the like are being used. The weight lifter lifts the barbells in a contraction portion of a stroke and, while the barbells are being held by the weight lifter, additional, eccentric weight is added to them by assistants. The weight lifter then lowers the barbells, now loaded with eccentric weight, in the relaxation portion of the stroke. With the barbells returned to the floor, the eccentric weight is manually removed, and the stroke may be repeated.
Conventional weight lifting and exercise machines are not well adapted for the addition of eccentric weight in the middle of a stroke. Thus, the weights used in the exercising machines shown in the two Uyada, et al. patents and in the Mezman patents can be engaged or disengaged only prior to the initiation of a stroke. The weights cannot be added during a stroke. The pneumatic exerciser shown in Ariel does provide for programming to maintain a constant force, velocity, or acceleration throughout a stroke or to vary any of these factors. However, the art is not cognizant of machine utilizing weights in which eccentric weight may be used in conjunction with concentric weights in varying the force to be overcome by the exerciser using the machine.